The invention relates to modular couplings which can be used for assembly or dismantling of frameworks, scaffoldings and like structures. More particularly, the invention relates to improvements in couplings which can be used to separably connect the end portions of braces, links and/or other types of frame members to each other for the purpose of erecting a skeleton frame, a scaffolding or another structure which must be readily assembled as well as readily dismantled.
A coupling of the above outlined character is disclosed in German Pat. No. 27 36 635 to MeroRaumstruktur. The patented coupling employs spherical female coupling members with radially inwardly extending tapped bores, and rod-shaped male coupling members with end portions carrying rotary bolts having externally threaded shanks which can be moved into mesh with the threads in a selected tapped bore. The means for rotating the bolts include hexagonal sleeves which surround the shanks of the bolts and are accessible at the free ends of the rods to facilitate rotation of the bolts by means of wrenches or other suitable tools. The patented couplings are complex and expensive because each sleeve must be non-rotatably mounted on the hexagonal portion of the respective shank and each bolt must be rotatably mounted in the end portion of the respective rod in a manner to prevent axial movements of the bolt. Furthermore, each sleeve is disposed forwardly of the respective end of the rod so that it contributes to the overall length of the respective coupling member. In addition, rotation of a bolt in order to drive its shank into the selected tapped bore of the female coupling member or to extract thenk shank from the tapped bore takes up a relatively long interval of time which is undesirable when a framework or scaffolding is to be assembled from a large number of male and female coupling members. The situation is aggravated if the framework is set up for a relatively short period of use, e.g., to serve as a stand at an exhibition, fair or auction, and must be taken apart after such relatively short period of use.
Published German patent application No. 26 33 147 of Endzweig discloses a modified coupling wherein the end portions of rod-shaped male coupling members carry hammerhead screws which can be inserted into and anchored in suitably configurated sockets of spherical female coupling members. Each screw has a shank which meshes with an internally threaded nut-like portion of the respective rod. Anchoring of a screw in the selected socket involves turning of the screw through 90 degrees, and the nut-like portion of the rod-shaped male coupling member must be rotated in order to move the front end face of the rod into abutment with the external surface of the spherical female coupling member. The coupling of Endzweig is complex and expensive. Moreover, the operator must exercise care to ensure that the angular position of the hammerhead of an inserted screw does not change during rotation of the nut in a direction to move the end face of the rod against the external surface of the female coupling member.
Published German patent application No. 28 09 811 of Gabriel discloses a coupling wherein the end portions of rod-like coupling members are bifurcated and each prong has an external recess which receives a portion of the wall surrounding the selected socket in a facetted female coupling member. The prongs must be pressed together in order to introduce them into a selected socket and are thereupon permitted to move apart in order to engage the female coupling member. Unintentional separation of the prongs of bifurcated end portions from the female coupling member is prevented by inserts which are placed between the prongs. The tips of the prongs are provided with inclined cam faces to facilitate penetration into a socket. However, the operator must exert a substantial force in order to push the prongs against each other prior to their extraction from the socket. Moreover, the slots between the prongs must be relatively long in order to enhance the resiliency of the prongs. The exposed portions of the slots detract from the appearance of the assembled coupling. All in all, dismantling of a structure embodying a number of just described couplings is a tedious and time-consuming procedure which is tiresome to the operator. Still further, the stability of the assembled coupling is not entirely satisfactory.
British Pat. No. 576,458 to Smith & Sons discloses a coupling wherein the female coupling member is a plate with a hole and two resilient tongues at one side of the plate. The plate-like male coupling member has a post with two lateral recesses for portions of the tongues. An elastic pad abuts the other side of the plate when the post is inserted through the hole and its recesses receive portions of the tongues. The post can be rotated by a key in order to expel the tongues from its recesses preparatory to extraction of the post from the hole of the plate-like female coupling member. A drawback of the patented coupling is that it cannot stand pronounced stresses which tend to separate the two coupling members. Moreover, the elastic pad is rigid with the post so that its bias must be overcome during turning of the key in order to expel the tongues from the recesses of the post.
German Pat. No. 24 26 973 to Mylseus discloses a coupling wherein an externally threaded post can be screwed into a selected tapped bore of a female coupling member in response to rotation of a sleeve which is secured to the end portion of a rod. The end portion of the rod has internal threads with a pitch which is different from that of threads in the tapped bore of the female coupling member. The sleeve has a polygonal outline and is rotatably mounted on the end portion of the rod. When the coupling operation is completed, the front end of the sleeve abuts the external surface of the female coupling member. A drawback of the patented coupling is that the post must be provided with two sets of threads, that a set of threads must be cut into the end portion of the rod and that each bore of the female coupling member is a tapped bore. Moreover, the connection between the sleeve and the post is complex because the post cannot rotate relative to but must be free to move axially of the sleeve.
Certain other conventional couplings employ combinations of features of the aforediscussed couplings. All heretofore known couplings share the drawback that they are costly, complex, unreliable and/or require too much time for assembly and/or dismantling. Thus, there exists an urgent need for a coupling which exhibits the advantages but does not embody the drawbacks of conventional couplings.